Cellular immunity and production of factors mediating this response (lymphokines) are frequently altered in patients with cancer. These alterations will be more easily quantitated and biochemical analysis of lymphokine production and function will be facilitated by the use of specific anti-lymphokine antibodies. Macrophage agglutination factor (MAggF) is a high molecular weight gelatin-binding lymphokine derived from antigen-\or mitogen-stimulated lymphocytes of guinea pigs, mice, or human beings. Because of multiple biochemical and antigenic similarities to fibronectin (FN), we previously proposed that it was a form of this protein. The FNs are a family of proteins involved in cell adhesion and regulation of cell morphology that, while showing some biochemical and functional differences among themselves, are generally closely-related to each other and display binding sites for gelatin, heparin, fibrin(ogen), and fibroblasts. During the past year, we have employed a number of monoclonal antibodies directed against plasma FN and against the human monocyte receptor for FN to demonstrate that MAggF shares domains with plasma FN, that MAggF activity is associated with the FN gelatin-binding domain, and that MAggF acts on macrophages through a FN receptor antigenically related to the FN receptor on the monocyte. On the basis of this characterization of MAggF as lymphokine FN, we will isolate MAggF from culture supernants by affinity chromatography over gelatin, gel filtration chromatography, and immunoadsorption. Purified MAggF will be compared with purified guinea pig plasma FN and used to raise monoclonal antibodies to assist in deciding if the two materials are truly identical. Anti-MAggF antibodies not cross-reactive with plasma FN will be used to evaluate the role of MAggF in cellular immunity in vivo and in vitro. (HF)